Flash spinning is an example of a spray process having very high issuance speed. Flash spinning processes involve passing a fiber-forming substance in solution with a volatile fluid, referred to herein as a “spin agent,” from a high temperature, high pressure environment into a lower temperature, lower pressure environment, causing the spin agent to be flashed or vaporized, and producing materials such as fibers, fibrils, foams or plexifilamentary film-fibril strands or webs. The temperature at which the material is spun is above the atmospheric boiling point of the spin agent so that the spin agent vaporizes upon issuing from the nozzle, causing the polymer to solidify into fibers, foams or film-fibril strands. Conventional flash spinning processes for forming web layers of plexifilamentary film-fibril strand material are disclosed in U.S. Pat. No. 3,081,519 (Blades et al.), U.S. Pat. No. 3,169,899 (Steuber), and U.S. Pat. No. 3,227,784 (Blades et al.), U.S. Pat. No. 3,851,023 (Brethauer et al.). However, the web layers formed by these conventional flash spinning processes are not entirely uniform.